Remote examination of tubular conduits is an activity well known in the chemical and power generation industries. Such industries utilize various conduit scanning methods in order to attempt to detect weaknesses or other potential failure points before an actual tube failure or leak situation occurs. Such early detection reduces unscheduled equipment outages, providing benefits in scheduling and overall cost savings.
It is well known that certain portions of a material-carrying conduit are more susceptible to wear, erosion, or other degradation and are therefore scanned with greater interest than other, less failure-prone portions. For example, in a nuclear steam generator utilizing a flow of heated primary fluid through a bundle of tubes in the shape of an inverted U for heating a surrounding secondary fluid, it is the curved portion of the tubular conduits which is most susceptible to corrosion or other degradation.
It has moreover been found that within the curved portion the innermost and outermost sections of the conduit wall are the areas in which stress cracking or corrosion are most likely to occur. It is therefore desirable to concentrate any scanning effort on the innermost and outermost radial portion of the conduit with respect to the axis of curvature. In order to provide this type of scan, probes have been utilized which traverse the interior of the individual conduits, each probe bearing one or more sensor means for determining the quality and status of the conduit wall. As the interior of the tubular conduits in a nuclear steam generator do not contain any reference points usable to orient such a probe, it has often been the practice to utilize multiple sensors spaced radially about the probe or to conduct repetitive scans of the curved conduit portion in order to increase the likelihood that the critical innermost and outermost conduit wall portions have been examined. As will be appreciated by those skilled in the art, the linear vertical portions of such inverted U tubes may be 30 feet in length or greater, thus making any attempt to orient the sensor probe by means of the driving cable a practical impossibility.
The use of multiple sensors, while increasing the area scanned, requires significantly greater effort to interpret the results of the individual sensors, due to the increased volume of data collected (much of which is not of interest). The use of multiple passes with a single sensor results in the same production of an abundance of scanning data and includes the additional disadvantage of possibly missing a critical portion of the conduit under consideration.
An effective device for scanning a curved conduit such as described above would orient the sensing means so as to pass over the desired portions of the conduit wall in a sensing relationship on the first pass therethrough, eliminating the need for multiple scans as well as the possibility that a critical portion of the conduit wall might not be measured.